1. Field of the Invention
The present invention relates generally to the field of digital communication systems and, more particularly, to the adaptive modification of modulated and coded schemes in a wireless digital communications systems.
2. Description of the Related Art
As the use of wireless communications continues to grow worldwide at a rapid pace, the need for frequency spectrum efficient systems that accommodate both the expanding number of individual users and the new digital features and services such as facsimile, data transmission, and various call handling features has become evident.
Current wireless data systems such as the cellular digital packet data (CDPD) system and the IS-130 circuit switched time division multiple access data system support only low fixed data rates which are insufficient for several applications. Since cellular systems are engineered to provide coverage at the cell boundary, the signal to interference plus noise ratio (SNR) over a large portion of a cell is sufficient to support higher data rates. Adaptive data rate schemes using bandwidth efficient coded modulation currently exist for increasing data throughput over the fading channels encountered in cellular systems. Increased data throughput is accomplished in these schemes by using bandwidth efficient coded modulation schemes with higher information rates. Disadvantageously, a practical problem to using these schemes is their inability to dynamically adjust the coded modulation to adapt to the channel conditions such as fading. Additionally, these schemes use interleaving and link layer retransmission that are not compatible with dynamic adaptation of the coded modulation.
Thus, there is a need for an adaptive scheme which will dynamically adjust the modulation, coding, interleaving, and data link re-transmission procedures to the channel conditions such as fading and provide higher data throughput.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In accordance with one aspect of the present invention, a system and method is provided for an adaptive channel coder and modulator, a channel decoder and demodulator connected to the adaptive channel coder and modulator, and a radio link protocol frame and channel decision unit connected to the adaptive channel coder and modulator.
These and other features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings and the appended claims.